I'm trying to find out how my machine works.
I prefer to use the [Redstone Ready] preset for Superflat.
However, the normal world is generated ignoring those settings.

Terralith's worldgen is done via datapacks, and due to a design choice by Mojang superflats still use the regular world's datapacks. You can disable it for a superflat if you want.

I searched quite a bit and couldn't figure out how to disable it.

you'd have to remove the mod

It's worth mentioning this issue on the terralith repo.